1. Field of the Invention
The invention relates to an ignition device in a motor vehicle for triggering a restraining device, in particular, a seat belt tightening device or airbags, wherein the ignition device comprises an ignition device housing or an ignition device body, an ignitor arranged in the area of the forward end of the ignition device, such as an ignition cap or an ignition resistor arranged in a powder chamber filled with a powder, as well as an energy transmitting device which extends from the rearward area of the ignition device opposite the ignitor to the ignitor and with which the ignitor can be triggered when heating occurs at the rearward area of the ignition device, especially in the case of a fire.
2. Description of the Related Art
An ignition device for triggering a restraining device is, for example, known from German patent DE 196 10 799 C1. In this ignition device, a support is provided with which ignition connector pins for receiving an ignition element are connected and which is furnished with electronic components such as an integrated circuit. The support can be formed as an MID support (MID=molded interconnect device). Such a support is, for example, formed by two different plastic material components which are connected to one another in a two-step injection molding process. The surface of one of the two plastic material components is metallized by an electro-chemical electroplating process while the surface of the other component does not accept such a metallization. By means of a corresponding embodiment of the arrangement of the two plastic material components, strip conductors for electronic components to be connected in an additional step can be provided by means of such a metallization by electroplating.
Other methods for manufacturing MID supports are also known, for example, so-called photo imaging technologies or film technologies. These technologies are, for example, described in the proceedings of the Third International Congress xe2x80x9cMolded Interconnect Devicesxe2x80x9d, Sep. 23-24, 1998, Erlangen, Germany (ISBN 3-87525-111-3). In each case, strip conductors are arranged on the injection-molded base body.
In AT 000 522 U1 an ignition device of the aforementioned kind mounted in a drive device of a restraining device is disclosed. The ignition device comprises an ignition cap which is mounted within a gas generator, i.e., extends into a chamber of the drive device which is filled with a propellant charge. For preventing ignition misfires, the ignition device has electronic components, in particular, inductive resistors. These components are relatively robust components in contrast to the more sensitive semiconductor components as, for example, integrated circuits.
Moreover, from U.S. Pat. No. 5,556,132 an ignition device of the aforementioned kind is known in which a device is provided by which, in the case of fire, it is ensured that, in the case of heating of the ignition device at its rearward area facing away from the ignitor, the ignitor is triggered before the housing becomes instable by heating. Otherwise, an uncontrolled triggering of the ignitor would be the result possibly causing parts of the now instable housing to be thrown off. This device comprises a pin which projects from the backside of the housing and extends through the housing to a chamber filled with a propellant charge in the area of the forward end of the ignition device. Across a portion of its length, the pin, beginning at the chamber filled with the propellant charge, is provided with a bore in which an auto ignition powder is provided. By heat transfer from the part of the pin projecting from the housing onto the auto ignition powder, the powder is ignited when its ignition temperature is surpassed so that the ignition device is triggered. A disadvantage of this ignition device is, in particular, the conductive connection of the pin into the powder chamber. This can carry the risk of a possible current flow through the pin and spark generation in the area of the propellant charge so that an impermissible triggering of the ignition device can occur. For example, such a current flow can be generated by electrostatic discharge or also in that the end of the pin projecting from the housing comes into contact with a voltage, for example, in the situation where the car body is subjected to a voltage during the course of repair work.
From German patent application DE 195 31 666 A1 a gas generator with an auto ignition device is also known for a heat exposure situation. A container is provided which is arranged in the powder chamber of the gas generator and is filled with an auto ignition powder. It is in a tight thermal surface contact with the upper part of the gas generator housing as well as with the oppositely positioned lower part of the gas generator housing. The ignition device of this gas generator is of a conventional configuration.
A further gas generator with an auto ignition device is known from U.S. Pat. No. 5,468,017. In this gas generator, the auto ignition powder is arranged in the area of the rearward wall of the gas generator housing. The ignition device of the gas generator is again of a conventional construction.
Moreover, from U.S. Pat. No. 5,429,386, a relatively complicated mechanical ignition device for the scenario of impermissibly high temperatures is described.
It is an object of the present invention to provided an improved ignition device of the aforementioned kind which, while having a relatively simple configuration, provides a high safety in a fire situation, on the one hand, and is at the same time insensitive with respect to electrostatic discharges or impermissible voltages on the car body, on the other hand.
In accordance with the present invention, this is achieved in that an energy transfer device is arranged in the interior of the ignition device member in the form of an ignition device housing or ignition device body (no separate housing), which has an insulated exterior, wherein the energy transfer device extends closely, preferably closer than 1 mm, to the external surface of the ignition device member (ignition device housing or ignition device body) at least in the area of the backside of the ignition device.
When the backside of the ignition device is heated during a fire situation, after melting of a thin coating which covers the rearward area of the energy transfer device, energy is transmitted from the energy transfer device to the ignitor. This results in triggering of the ignition device in a timely fashion before the ignition device housing or ignition device body can become instable.
An energy transfer device could be realized by a heat conducting element or, for example, also by a pyrotechnical device which extends from the rearward area of the ignition device to the ignitor and can be, for example, a match cable or a hollow space filled with a pyrotechnical material.
In an advantageous embodiment of the invention, the ignition device has an MID support for the electronic components which is provided with metallized strip conductors for connecting electronic components, wherein the heat conducting device comprises at least one metallized area of the MID support or is formed by at least one metallized area of the MID support.